This invention relates to a method of modifying the crystalline structure of a sheet of semiconductor material. More particularly, this invention relates to a method for producing silicon sheets useful for the production of solar cells.
Semiconductor devices are generally fabricated from wafers of monocrystalline silicon. Various procedures for preparing monocrystalline silicon wafers have been described in the prior art. Thus, the Czochralski method comprises pulling a monocrystalline rod from a pool of liquid produced by melting polycrystalline silicon. Another method, known as the float zone technique, comprises pulling a monocrystalline rod from a liquid region, formed by localized heating, within or on top of an ingot of polycrystalline material. Both techniques produce a monocrystalline rod which must be sawed into slices and further processed by lapping, polishing, and/or etching to produce wafers suitable for the production of semiconductor devices. Another prior art method, directed to pulling single crystals in the form of long flat strips from a melt, is disclosed in U.S. Pat. No. 3,096,158. However, this method requires the use of a seed crystal, a melt, a concentrator element, a multiple-turn coil and a shield.
With the present need for new energy sources, many suggestions have revolved around the use of solar energy. One way of utilizing this type of energy is with solar cells, whereby radiant solar energy is converted directly to electrical energy. However, systems using solar cells will require large amounts of semiconductor material, that is, generally monocrystalline silicon. If such systems are to become commercially acceptable, such silicon must be obtainable at a cost far less than present costs for monocrystalline silicone wafers.